The present invention relates to a header or header box for a heat exchanger and to a heat exchanger provided with this header.
The heat exchangers in question are intended, although not exclusively, to be fitted to vehicles, and in a preferred application they form the condensers provided in the air conditioning loops or circuits of vehicles, or the radiators provided in the cooling loops or circuits of engines. However, other applications of these heat exchangers may also be envisaged without departure from the scope of the invention.
Generally, a heat exchanger for a heat loop of this type comprises a bundle of parallel tubes and two headers to which the corresponding ends of the parallel tubes are connected in a fixed and sealed way. Thus the fluid, for example the coolant used in the loop, can flow through the tubes from the upstream header, facing the compressor, toward the downstream header, facing the expander, the fluid being made to pass from the vapor phase to the liquid phase by the external forced air flow which sweeps the tubes whose surface area, increased by the addition of disrupters or dividers in the tubes and/or between the tubes, optimizes the heat exchange.
In the present case, the exchangers are of the type produced by brazing, and the headers used may be designed in two parts, being known as “two-part headers” or “two-part header boxes”.
This type of header, which has a tubular overall shape, includes:
a header plate with a longitudinally open wall, provided with slots intended to receive the corresponding ends of the parallel fluid flow tubes; and
a cover which, after assembly, closes the longitudinal opening of the header plate, and which has a wall including at least one external collar delimiting a hole for the flow of fluid.
Additionally, a connecting flange is attached to the header in a known way in order to provide a connection between the header and a conduit leading to the expander or compressor of the loop concerned. In particular, the connecting flange has an inner fluid passage which is made to face the hole in the header provided for this purpose, and the flange generally surrounds the external collar of the cover. The flange is fastened by crimping, the edges of the header plate being bent onto the corresponding edges of the flange which rests on the cover. The exchanger is placed in a brazing furnace to ensure that, notably, the header plates, the header covers and flanges, and the tubes are assembled together and sealed.
Other flanges may also be fitted on these headers, such as flanges for fastening the exchanger to supporting parts of the vehicle, including, notably, other adjacent exchangers or the chassis of the vehicle.
Satisfactory results are obtained in this way, notably because of the collar which enables the flange to be positioned and brazed as a result of the provision of coating on the collar, and because of the crimping of the whole assembly, but this solution using a collar also gives rise to problems regarding the efficiency of the exchanger.
This is because the double thickness of the collar wall measured along the diameter tends to significantly reduce the available passage cross section. Consequently there is an increased pressure drop at this point.
This becomes more critical in the aforesaid case of a condenser-type exchanger in which the flange is crimped between the cover and the bent edges of the header plate of each header. Therefore, since the inside diameter of the collar, that is to say the diameter of the hole for the flow of coolant, is restricted by the width of the header (which cannot be increased, owing to unavoidable space constraints), or, in other words, is determined by the crimping width of the two edges of the plate which are bent toward one another, by the two thicknesses of the flange delimiting the passage, and by the two diametric thicknesses of the wall of the collar which extends from the cover, the cross section of the hole in the collar is limited.